Method and apparatus for real time testing of DTV antenna transmitting systems in time domain under full power

ABSTRACT

A real time apparatus for testing a DTV antenna transmitting system, wherein the DTV antenna transmitting system transmits an original signal from a DTV transmitter to a DTV transmitting antenna, is disclosed that includes a probe, wherein the probe is connected in series with the DTV antenna transmitting system, and senses signals traversing the DTV antenna transmitting system. An error detector of the testing apparatus compares the received signal to the original signal to identify the magnitude and location of errors.

The present application claims priority from U.S. patent applicationentitled, Method And Apparatus For Real Time Testing Of DTV AntennaTransmitting Systems In Time Domain Under Full Power, filed Apr. 5,2002, having Ser. No. 10/116,112.

FIELD OF THE INVENTION

The present invention relates generally to an antenna testing system.More particularly, the present invention is directed to a method andapparatus for real time testing of digital television (DTV) antennatransmitting systems.

BACKGROUND OF THE INVENTION

The Federal Communications Commission has required televisionbroadcasters to transition from their current National Television SystemCommittee (NTSC) analog antenna systems to DTV antenna systems. DTVtechnology allows for the transmission of television programming havinghigher resolution pictures and better sound quality than NTSC analogantenna systems. DTV systems also allow broadcasters to transmit morethan one signal per channel, and thus, deliver more than one televisionprogram per station.

Test receivers exist for identifying problems in the transmission of aDTV signal from the DTV transmitting antenna to a particular point ofreception, but problems can also occur in the transmission of the DTVsignal from a DTV transmitter to the DTV transmitting antenna thatprevent a signal generated by the DTV transmitter from reaching the DTVtransmitting antenna.

Echoes are reflected signals that occur when the impedance is notproperly matched between components of the DTV transmitting system andcan be an indicator of potential problems in the transmission of a DTVsignal. The echo/reflected signals “add to” or “subtract from” thesignal being transmitted from the DTV transmitter to the DTVtransmitting antenna, and, as such, increase or decrease the level ofthe DTV signal. Although echoes commonly occur during the transmissionof a DTV signal, they will cause problems if their magnitude increasesto a level that interferes with the transmission of the DTV signal.

When echo levels exceed an acceptable threshold, the signal received bythe transmitting DTV antenna may differ greatly from the original signalthat was sent by the DTV transmitter. The echoes may even cause the DTVsignal and/or sound corresponding to a television program to be lostcompletely, and disrupt television service to a viewer. Testing devicesare needed to analyze the performance of a DTV antenna transmittingsystem from the DTV transmitter to the transmitting antenna, and toprovide data about the performance of the DTV antenna transmittingsystem, so that failures can be avoided. Methods exist for testing DTVtransmitting systems that are capable of identifying whether or notechoes are occurring within a transmitting system. The conventionalmethod of testing DTV transmitting systems requires going off-air andshutting down the DTV transmitting system, which can be costly, toconnect the testing device to the transmission line. The conventionalmethod of testing DTV transmitting systems utilizes a testing device,such as a network analyzer, that is connected to the transmission linevia a connector/adapter. A low power test signal is then sent by thetransmitter, and the network analyzer analyzes the signal received. Thenetwork analyzer is able to ascertain the magnitude of the problem(i.e., how much of the test signal was lost up to the point at which thenetwork analyzer is connected) and the source or location of the signalloss. However, the network analyzer cannot be utilized to test DTVtransmitting systems in real time while operating under full power.Additionally, the network analyzer is limited to a resolution ofapproximately a hundred feet if used with 6 MHz bandwidth, and thusunable to identify potential problems that are less than a hundred feetapart.

Another method of testing DTV antenna systems is described in U.S. Pat.No. 6,212,286 to Rott et al. (hereafter “Rott”) which discloses a methodof testing a DTV antenna transmitting system in real time and under fullpower. Rott involves a method for testing an antenna system that enablesthe source/location of a problem to be identified by aiming an infraredcamera at the component of the transmitting system to be tested whilethe component is in full operation.

The infrared camera records a thermal image of the test object. When thetemperature of a portion of the thermal image is extremely high whencompared to the remainder of the thermal image, the portion of the testobject corresponding to the high temperature area on the thermal imageis likely to be the source of the problem. Typically, a sharp increasein temperature is an indicator of a malfunctioning component. Thus, thearea of the thermal image where there is a temperature increase can bematched to the area of the component that was tested.

The thermal image generated from the testing method of Rott revealsextreme temperature gradients. If an echo is created, that only causes asmall increase in temperature, the echo may go undetected by theinfrared camera of Rott. As a result, DTV service to consumers may beinterrupted by the effects of the undetected echo signal.

Accordingly, it is desirable to provide a real time method for testingDTV antenna transmitting systems from the DTV transmitter to the DTVtransmitting antenna that is operable under full power.

Further, it is desirable to provide a method for real time testing ofDTV antenna transmitting systems that can identify the magnitude and thelocation of existing and/or potential problems.

Further, it is desirable to provide a method for testing a DTV antennatransmitting system that minimizes time and cost in identifying andresolving a problem that occurs within a DTV antenna transmittingsystem.

SUMMARY OF THE INVENTION

In one aspect of the present invention a real time apparatus for testinga DTV antenna transmitting system, where the DTV antenna transmittingsystem transmits an original signal from a DTV transmitter to a DTVtransmitting antenna is provided that includes a probe, wherein theprobe is connected in series with the DTV antenna transmitting system,and wherein the probe senses a signal traversing the DTV antennatransmitting system and generates a received signal, and an errordetector which compares the received signal to the original signal toidentify an error, wherein the error detector identifies the magnitudeand location of the error, and a processor, wherein the processorcompares the magnitude of the error to a predetermined value.

In another aspect of the present invention a real time apparatus fortesting a DTV antenna transmitting system, where the DTV antennatransmitting system transmits an original signal from a DTV transmitterto a DTV transmitting antenna is provided that includes a means forsensing a signal traversing the DTV antenna transmitting system in realtime and generating a received signal, and a means for comparing thereceived signal to the original signal to identify an error, and whereinthe comparing means identifies the magnitude and location of the error.

In yet another aspect of the present invention, a method for testing aDTV antenna transmitting system, wherein the DTV antenna transmittingsystem transmits an original signal from a DTV transmitter to a DTVtransmitting antenna is provided that includes sensing a signaltraversing the DTV antenna transmitting system in real time andgenerating a received signal, and comparing the received signal to theoriginal signal to identify an error, and identifying the magnitude andlocation of the error.

There has thus been outlined, rather broadly, the more importantfeatures of the invention in order that the detailed description thereofthat follows may be better understood, and in order that the presentcontribution to the art may be better appreciated. There are, of course,additional features of the invention that will be described below andwhich will form the subject matter of the claims appended hereto.

In this respect, before explaining at least one embodiment of theinvention in detail, it is to be understood that the invention is notlimited in its application to the details of construction and to thearrangements of the components set forth in the following description orillustrated in the drawings. The invention is capable of otherembodiments and of being practiced and carried out in various ways.Also, it is to be understood that the phraseology and terminologyemployed herein, as well as the abstract, are for the purpose ofdescription and should not be regarded as limiting.

As such, those skilled in the art will appreciate that the conceptionupon which this disclosure is based may readily be utilized as a basisfor the designing of other structures, methods and systems for carryingout the several purposes of the present invention. It is important,therefore, that the claims be regarded as including such equivalentconstructions insofar as they do not depart from the spirit and scope ofthe present invention.

BRIEF DESCRIPTION OF FIGURES

FIG. 1 is a block diagram of a system for testing, monitoring and/oroptimizing an antenna system in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE PRESENTINVENTION

Referring now to FIG. 1, a testing device 10 is provided for testing aDTV antenna transmitting system 12 in accordance with the presentinvention. In an exemplary embodiment of the present invention, thetesting device 10 detects errors, such as those caused by echoes, in theDTV antenna transmitting system 12. The DTV antenna transmitting systemincludes a DTV transmitter 14, a transmission line 16 and a DTVtransmitting antenna 18.

In an exemplary embodiment of the present invention, the testing device10 includes a tuner 20, an echo/error detector 22, and an equalizer 24.A probe 26, processor/central processing unit (CPU) 28, a display 30 andan input device 32 are connected to the testing device 10 to provide forinput and output of data from the testing device 10.

The probe 26 is utilized to couple the testing device 10 to any point inthe DTV antenna transmitting system 12. The probe 26 detects the signalsthat traverse the point in the DTV antenna transmitting system 12 towhich the probe 26 is coupled. In exemplary embodiments of the presentinvention, the probe 26 is a voltage probe, current probe, singledirectional coupler or dual directional coupler. A directional coupleris a device that is utilized to sample a forward (incident) and/orbackward (reflected) wave in a transmission line.

In an exemplary embodiment of the present invention, the probe 26 isconnected in series with the DTV antenna transmitting system 12, suchthat the testing device 10 can monitor and/or test the signalstraversing the DTV antenna transmitting system 12 continuously, at aninstant point in time, and/or during discrete intervals in time. In anexemplary embodiment of the present invention the probe 26 and testingdevice 10 may be provided as part of the DTV antenna transmitting system12.

In an exemplary embodiment of the present invention, the signal that istransmitted from the DTV transmitter 14 to the DTV transmitting antenna18 is transmitted at a constant voltage level. The DTV signal ismodulated at the DTV transmitter 14 by an eight-level VSB (8-VSB)standard, which is a modulation format that is utilized for theterrestrial transmission of DTV. The modulation format was establishedas the standard for DTV transmission in the United States by theAdvanced Television Systems Committee (ATSC). The 8-VSB standard isconsidered an effective method for the transmission of DTV programmingbecause it allows for either transmission of HDTV, or more than onestandard DTV program (multicasting) and/or the transmission of otherdata along with a television program (data casting).

The tuner 20 is utilized to automatically or manually select a signal tobe tested, monitored and/or optimized from the signals in the channelthat are being transmitted from the DTV transmitter 14 to the DTVtransmitting antenna 18 and sensed by the probe 26. In exemplaryembodiments of the present invention, the tuner is utilized todemodulate the DTV signal.

The probe 26 senses the signals in the frequency domain, and outputs awaveform that indicates the magnitude of the signal as a function offrequency. In an exemplary embodiment of the present invention, the CPU28 is coupled to the probe 26. The input device 32 is utilized tocontrol the probe's level of sensitivity, i.e., the amount of the DTVsignal that the probe is able to sense.

The recovered/received DTV signal that is sensed by the probe 26 may notcorrespond to the original signal that was transmitted by the DTVtransmitter 14 if errors/echoes were generated during the transmissionof the DTV signal from the DTV transmitter 14 to the DTV transmittingantenna 18. When echoes/error occur, the DTV signal will have varyingsignal levels, instead of one signal level.

The echo/error detector 22 is utilized to identify the occurrences oferrors/echoes in the recovered signal by identifying where the DTVsignal deviates from a constant level. The error detector 22 firstidentifies the baseband voltage by identifying the primary voltage fromwhich the DTV signal is deviating. The levels of the recovered DTVsignal is then compared to the identified baseband of the original DTVsignal.

The error detector 24 generates an echo signal/error correction signalthat corresponds to the differences between the baseband level of theoriginal signal and the levels of the recovered signal. Accordingly, theamount of any “increases to” or “decreases from” the level of theoriginal signal transmitted by the transmitter are attributed toechoes/errors, and the magnitude of the echoes/errors are known.

In an exemplary embodiment of the present invention, the display 30 isutilized to display the original signal, the recovered signal, and/orthe echo/error correction signal. The display is also utilized todisplay the echo level versus distance. In exemplary embodiments of thepresent invention, the magnitude of the signal is expressed, forexample, in decibels, as a voltage standing wave ratio (VSWR) and/or bya reflection coefficient.

Further, the location of the error/echo can be ascertained. The CPU 28is utilized to determine the location of the error/echo along thetransmission path from the DTV transmitter 14 to the DTV transmittingantenna 18. The CPU 28 is utilized to calculate the distance the echo isin air from, for example, the DTV transmitter 14, by utilizing theequation distance=speed time.

In an exemplary embodiment of the present invention, the distance ismeasured in feet or meters, the speed is 984 feet per microsecond or299.9232 meters per micro second.

Accordingly, the location of the echo signal, relative to the DTVtransmitter, can be identified by multiplying the speed of the signal bythe time of the occurrence of the echo, which can be deduced from theecho signal generated. Thus, the distance can be easily calculated, andthe magnitude of the echo signal can be displayed as a function ofdistance from a point in the DTV transmitting system 12.

In an exemplary embodiment of the present invention the CPU 28 is aprocessor that is utilized to convert the unit of measurements that willbe utilized to display for example, the original signal, receivedsignal, echo signal and or the echo signal level versus distance. TheCPU 28 can be utilized, for example, to convert the magnitude of thesignal level to decibels, a VSWR or a reflection coefficient.

In an exemplary embodiment of the present invention, the error/echodetector 22 is coupled to an equalizer 24. The equalizer 24 utilizes a192-tap-decision feedback filter to generate a correction pixel that, ifutilized, would reduce distortion in a signal caused by an echo/error.

The filter takes the coefficient weighted average of a finite number ofsource pixels (in this case 192), which are referred to as taps, tocalculate the replacement/correction pixel for the pixel that is out ofplace because of the echo.

In an exemplary embodiment of the present invention, the filtersamples/taps the DTV signal every ninety-three nano seconds. The errordetector 22 of the present invention ascertains the magnitude andlocation of the echo signal by extracting the tap data, from thecorrection pixel data. The tap data corresponds to the energy of theecho signals. It should also be understood that other filters, whichhave a finite number of taps, may be utilized.

In an exemplary embodiment of the present invention, software isutilized, by for example, the CPU 28 to determine whether the echo/errorsignals are within an acceptable threshold. In another exemplaryembodiment of the present invention, the software outputs an audible orvisual alarm to alert a user of the test device 10 when theechoes/errors are at a level that threatens the performance of the DTVtransmitting system 12.

In an exemplary embodiment of the present invention, the testing device10 extracts the correction pixel data from the equalizer 24 andconstructs or generates an echo/error correction signal that includesdeviations, from the original signal of a constant voltage level, whichcorrespond to the correction pixels. In an exemplary embodiment of thepresent invention, the equalizer 24 is an ATSC/8-VSB TV test receiver,either EFA models 50 or 53, by Rohde & Schwarz of Muinchen, Germany thathas a resolution within forty-seven feet.

In an exemplary embodiment of the present invention, the tuner 20, errordetector 22, and equalizer 24 are incorporated into the testing device10.

It should be understood that the tuner 20, equalizer 24, probe 26, CPU28, display 30, and input device 32 may exist separately from the errordetector 22, either alone or in combination with another device.

It should also be understood that a testing device 10 in accordance withthe present invention can also be utilized with other systems, forexample, cellular systems, personal communications systems, andsatellite systems.

By utilizing a testing device 10 in accordance with the presentinvention, which identifies the magnitude and location or errors/echoesin real time and under fall power, a user of the testing device canidentify errors/echoes that are of a magnitude that could interfere withthe transmission of the DTV signal from the DTV transmitter 14 to theDTV transmitting antenna 18 without shutting down the DTV transmittingsystem. A user of the testing device 10 of the present invention canalso adjust the components of the DTV transmitting system 12, whichcorrespond to the location of where the error signal is occurring, tooptimize the performance of the DTV transmitting system.

The many features and advantages of the invention are apparent from thedetailed specification, and thus, it is intended by the appended claimsto cover all such features and advantages of the invention which fallwithin the true spirit and scope of the invention. Further, sincenumerous modifications and variations will readily occur to thoseskilled in the art, it is not desired to limit the invention to theexact construction and operation illustrated and described, andaccordingly, all suitable modifications and equivalents may be resortedto, falling within the scope of the invention.

1. A real time apparatus for testing a DTV antenna transmitting system,wherein the antenna transmitting system transmits an original signalfrom a DTV transmitter to a DTV transmitting antenna, comprising: aprobe, wherein the probe is connected in series with the DTV antennatransmitting system, and wherein the probe senses a signal traversingthe DTV antenna transmitting system in real time and generates areceived signal; an error detector which compares the received signal tothe original signal to identify an error, and wherein the error detectoridentifies the magnitude and location of the error; and a processor,wherein the processor compares the magnitude of the error to apredetermined value.
 2. The apparatus of claim 1, further comprising atuner, wherein the tuner receives the received signal.
 3. The apparatusof claim 1, wherein the processor outputs an alarm.
 4. The apparatus ofclaim 1, further comprising an equalizer, wherein the error detector iscoupled to the equalizer and, wherein the equalizer compares thereceived signal to the original signal.
 5. The apparatus of claim 4,wherein the equalizer utilizes a filter to identify the error.
 6. Theapparatus of claim 5, wherein the filter is a 192-tap-decision-feedbackfilter.
 7. The apparatus of claim 1, wherein the error detectorgenerates an error signal and wherein the error signal is an echosignal.
 8. The apparatus of claim 1, further comprising a display. 9.The apparatus of claim 4, wherein the equalizer is an ATSC/8-VSB EFAtest receiver manufactured by Rohde and Schwarz.
 10. The apparatus ofclaim 9, wherein the error detector extracts the error signal from theequalizer.
 11. The apparatus of claim 10, wherein the CPU changes theunits of measurements utilized by the equalizer.
 12. A real timeapparatus for testing a DTV antenna transmitting system, wherein the DTVantenna transmitting system transmits an original signal from atransmitter to a transmitting antenna, comprising: means for sensing inreal time a signal traversing the DTV antenna transmitting system andgenerating a received signal; and means for comparing the receivedsignal to the original signal to identify an error, and wherein thecomparing means identifies the magnitude and location of the error. 13.The apparatus of claim 12, further comprising a means for selecting thereceived signal to be tested.
 14. The apparatus of claim 12, furthercomprising a means for recovering the original signal from the receivedsignal.
 15. The apparatus of claim 12, wherein the sensing means is avoltage probe.
 16. The apparatus of claim 12, wherein the sensing meansis a directional coupler.
 17. The apparatus of claim 12, wherein thecomparing means is an equalizer.
 18. A method for testing a DTV antennatransmitting system, wherein the DTV antenna transmitting systemtransmits an original signal from a DTV transmitter to a DTVtransmitting antenna, comprising: sensing a signal traversing the DTVantenna transmitting system in real time and generating a receivedsignal; and comparing the received signal to the original signal toidentify an error; and identifying the magnitude and location of theerror.
 19. The apparatus of claim 18, further comprising: analyzing theerror utilizing software; and determining the potential effect of theerror on the DTV transmitting system.
 20. The apparatus of claim 18,wherein the error is an echo.